This invention relates to a device for cutting, retaining and tucking the weft end to provide a selvedge along the yarn feeding side of a woven fabric.
Known are various devices for application to shuttleless looms, which are intended to cut and retain the weft yarn to allow successive tucking thereof in order to form the selvedge.
Such prior art devices substantially comprise a cutting assembly, between the blades whereof the weft yarn is brought by a driven gripper.
That cutting assembly cuts the yarn and retains it by means of an elastic device, usually a spring, until a hook picks it up and tucks it into the shed.
Other devices designed to perform that same operation employ pneumatic means, such as air suction nozzles, to retain the cut yarns.
Both approaches, however, are not free of operational drawbacks and constructional complexity.
In particular the last-mentioned devices, employing suction air, are not very effective and are hardly suitable for pneumatically separating the weft ends.
By contrast, the former while providing a satisfactory yarn cutting and retaining action, by the very reason of its retaining the yarn through the continued action of an elastic pressure means, has a tendency to foul very quickly.
In fact, particularly with hairy yarns, as the cut end is picked up by the hook, it is withdrawn from a retaining means which keeps exerting its pressure without opening.
The resulting effect is that part of the yarn remains jammed in the pick up member, thus forming within a short time a hair staple which impairs the device proper operation.
At this time, it becomes necessary to stop and clean the machine.
A further drawback comes from the fact that no provision is made for generally adjusting the cutting device to suit the type of yarn, the slay reed movement and the temple position.
Another difficulty originates from the fact that all the movements of these devices are normally actuated by means of spring biassed cams; owing to the high speed reached by modern looms, the biassing springs are in fact so highly strained that their operation is sometimes critical and unreliable, such as to undergo frequent failure.